¹Yutong Ma, ²Zhuang Guo, ³Aicheng Zhang, ⁴Jingjing Niu, ¹Shan Qin
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.01.037]
¹Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing 100871, China
²State Key Laboratory of Continental Evolution and Early Life, NWU-HKU Joint Center of Earth and Planetary Sciences, Department of Geology, Northwest University, Xi’an 710069, China
³School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
⁴State Key Laboratory of Tibetan Plateau Earth System Science, Resources and Environment (TPESRE), Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
Copyright Elsevier

Nanophase iron particles are ubiquitous in lunar soils and are largely attributed to space weathering; however, no nanophase iron particles formed in lunar crystalline minerals via impact events have been reported. Their growth, migration, spatial distribution, and interactions with host minerals under impact remain poorly understood. Here, we report the discovery of impact-induced dusty olivine clasts (containing nanoscale to submicron iron metal particles) in the lunar breccia meteorite Bechar 012. These clasts encapsulate a comprehensive record of iron particle formation and distribution within their crystalline host. Their well-preserved state provides a clear snapshot of the microscopic mineral processes often obscured in more heavily processed soils or breccias, making Bechar 012 an ideal natural sample for study. Crystallographic orientation analysis suggests that these dusty olivine grains undergo plastic deformation, with iron metal particles concentrated within the deformed regions, indicating a correlation between deformation microstructures and iron metal particle formation. We propose a three-step model for the formation of dusty olivine and the iron metal particles therein: (1) impact-induced plastic deformation of olivine; (2) sub-solidus olivine decomposition (Fe2SiO4 = 2Fe + SiO + 3/2O2) within partially amorphous zones, leading to the nucleation of nanosized iron metal particles, with SiO and O2 diffusing away through disordered pathways (e.g., partially amorphous zones, dislocations and pores) in the deformed olivine; and (3) capture of particles by migrating dislocations, followed by aggregation and oriented attachment (OA)-driven growth along the olivine lattice at dislocations and subgrain boundaries, resulting in the formation of submicron-sized iron metal particles. These processes indicate an equilibrium shock pressure below 16 GPa, with temperatures between 1000 °C and 1650 °C. These results confirm the pivotal role of impact-induced olivine deformation in facilitating the formation, migration, and growth of iron metal particles and highlight the significance of OA in their coarsening. The discovery of impact-induced iron metal particles in the lunar meteorite indicates that these particles can be broadly formed within crystalline minerals, rather than being limited to the amorphous rims of lunar regolith minerals and glassy impactites, while also offering a potential explanation for the lunar magnetic anomalies.